Big Boy

The Big Boys were specifically designed to pull a 3,600 short ton (3,300 t) freight train over the long 1.14% grade of the Wasatch Mountains in Utah. They were designed for stability at 60 miles per hour (100 km/h). They were built with a heavy margin of reliability and safety, as they normally operated well below that speed in freight service. Optimal horsepower was achieved at about 35 mph (56 km/h); optimal tractive effort, at about 10 mph (16 km/h).